Kiyotsugu
Rich and influential amongst his class, Kiyotsugu used to tease Rikuo about youkai until he was saved by “night” Rikuo years ago. He now has an obsession with youkai, even to the point of wanting to be kidnapped.
He has a high opinion of Night Rikuo, calling him “my idol, the emperor of the night” and citing how Night Rikuo has often saved humans.
He autonomously declared the formation of the Kiyojuji Paranormal Investigation Squad consisting of Rikuo and his classmates and regularly organizes youkai-oriented excursions. He has a website called “Youkai Knowledge” and styles himself a youkai hunter.
A running gag in the series is how he always just manages to miss having youkai encounters.